Background: Self-concept is seen as both an outcome of sociocognitive and emotional development, and a factor in social and mental health outcomes. Although the contribution of attachment experiences to self-concept has been limited to quality of primary attachment relationships, little is known of the effects of disturbed attachment on self-concept in institutionalized children. Thus, the current study examined associations between disturbed attachment behaviours in institutionalized children and self-concept, testing limited exploration as an explanatory factor. Methods: Thirty-three institutionalized children, aged 4–12, participated in a multimethod and multi-informant assessment of disturbed attachment behaviours (i.e., Disturbances of Attachment Interview and Behavioral Signs of Disturbed Attachment in Young Children), self-concept (i.e., Pictorial Scale of Perceived Competence and Social Acceptance for Young Children), and exploratory behaviours (i.e., Student Exploratory Behaviours Observation Scale). Analyses were conducted using bootstrapping techniques. Results: Global self-concept converged with teacher-rated children's self-concept, except for physical competence domain. Disturbed attachment behaviours were identified in 62.5% of the children, and this was associated with lower levels of exploration and lower scores on self-concept, compared with children without disturbed attachment behaviours. Furthermore, exploratory behaviours mediated the effects of disturbed attachment behaviours on self-concept. Conclusions: Institution-reared children with disturbed attachment behaviours were likely to have a negative perception of self and one's own competences. Limited exploratory behaviours explained this linkage. Targeting disordered attachment in children reared in institutions and their caregivers should become a high priority as a means for preventing socioemotional development issues.